1. CNC machine tools The CNC machine tools generally consist of input and output devices, numerical control devices (CNCs), servo units, drive units (or actuators), programmable controllers (PLCs) and electrical control devices, auxiliary devices, machine tools and measuring devices. composition.
(1) Input and output devices of CNC machine tools. It is an interactive device for machine tool numerical control system and operators to exchange information and realize human-machine dialogue.
The function of the input device is to change the numerical control code on the program carrier into a corresponding electrical pulse signal, which is transmitted into and stored in the numerical control device. At present, the input device of the numerical control machine tool has a keyboard, a disk drive, an optical reader, etc., and the corresponding program carrier is a magnetic disk and a punched paper tape. The output device is a display, and has a CRT display or a color liquid crystal display. The function of the output device is that the numerical control system provides the operator with the necessary information through the display. The displayed information can be the program being edited, coordinate values, and alarm signals.
(2) Numerical control device (CNC device). It is the core of the computer numerical control system and is composed of hardware and software. It receives the pulse signal from the input device. After the signal is compiled, operated and logically processed by the system software or logic circuit of the numerical control device, various signals and commands are output, and various parts of the machine tool are controlled to make the specified Order action. The most basic of these control signals is the feed rate, feed direction and displacement command of each coordinate axis (ie, each actuator for the feed motion) (sent to the servo drive system to drive the actuator for the feed motion). There are also the shifting, reversing and starting and stopping signals of the main shaft, selecting and exchanging the tool command signals of the tool, controlling the coolant, starting and stopping the lubricating oil, controlling the loosening and clamping of the workpiece and the machine tool parts, and controlling the indexing table indexing. Auxiliary command signals, etc.
The numerical control device mainly includes a microprocessor (CPU), a memory, a local bus, peripheral logic circuits, and an interface connected with other components of the CNC system.
(3) Programmable Logic Controller (PLC). CNC machine tools complete the control functions through CNC and PLC. Among them, CNC mainly performs functions related to digital calculation and management, such as editing of part program, interpolation operation, decoding, position servo control of tool movement and so on. The PLC mainly performs some actions related to the logic operation. It receives the control information of the CNC (auxiliary function), S (spindle speed), T (selection knife, tool change) and other switching action information, and performs the switching action information. Decoding, conversion into corresponding control signals, control auxiliary devices to complete the corresponding switching actions of the machine tool, such as workpiece clamping, tool replacement, coolant switching and other auxiliary actions. It also receives commands from the machine's operator panel, on the one hand directly controlling the machine's actions (such as manually operating the machine), and on the other hand sends a portion of the commands to the CNC for control of the machining process.
In the FANUC system, a PLC dedicated to controlling a machine tool is referred to as a PMC, which is called a programmable machine tool controller.
("Servo unit. The servo unit receives the speed and displacement commands from the numerical control unit. These commands are converted and amplified by the servo unit and converted into the speed, direction and displacement of the machine feed motion by the drive unit. Therefore, the servo unit is the numerical control unit. The link with the machine body, which amplifies the weak command signal from the numerical control device into a high-power signal for controlling the drive device. The servo unit is divided into a spindle unit and a feed unit, and the servo unit has an open-loop pump for its system. Division, semi-closed loop system and closed loop system.
(5) Drive unit. The driving device changes the command signal amplified by the servo unit into mechanical motion, drives the machine tool table through the mechanical connecting component, and makes the working table accurately position or strictly move according to the prescribed trajectory, and the shape, the size and the precision meet the requirements. Components. At present, the commonly used driving devices are DC servo motors and AC servo motors, and AC servo motors are gradually replacing DC servo motors.
The servo unit and the drive unit are collectively referred to as the servo drive system. It is the power unit for the machine tool. The instructions of the computer numerical control unit are implemented by the servo drive system. The servo drive unit includes the spindle drive unit (mainly controlling the speed of the spindle). Give the drive unit (mainly controlling the speed and position of the feed system). The servo drive system is an important part of CNC machine tools. In a sense, the function of CNC machine tools mainly depends on the numerical control device, and the performance of CNC machine tools mainly depends on the servo drive system.
(6) Machine body. That is, the mechanical components of the CNC machine tool, including the main moving parts, the feed motion execution parts (workbench, carriage and its transmission parts) and support parts (bed, column, etc.), including cooling, lubrication, indexing and clamping Auxiliary devices with tight functions. The CNC machine tools of the machining center class also have tool magazines for storing tools, robots for exchanging tools, and the like. The components of CNC machine tools are similar to those of ordinary machine tools. Due to the high speed, high precision, large cutting amount and continuous machining requirements of CNC machine tools, the mechanical components have higher requirements on accuracy, rigidity and vibration resistance.
In addition, in order to ensure the full play of the functions of CNC machine tools, there are also some auxiliary systems, such as cooling system, lubrication system, hydraulic (or pneumatic) system, chip removal system, protection system and so on.